The subject innovation relates generally to thyristors and in particular to controlling switching noise associated with an inductively loaded thyristor.
Conventionally, speed of transition from an off state to an on state of a thyristor is not controllable once the device is gated (e.g., switched). Voltage across the thyristor will rapidly change from an open circuit to a conducting voltage. If an inductive load connected to a power line is being switched, a high rate of voltage change (dv/dt) can occur, and can be coupled through the load to the power line, and such high rate of change can cause an undesirable level of noise emissions from the device to the power line. Many jurisdictions regulate and limit magnitude of noise allowed to be manifested by a device to power lines. When noise emissions generated by a device exceeds such limits, implementation of some form of noise mitigation is required.
Conventionally, to mitigate conducted noise associated with thyristors during change of state, a filter is employed between the noise source and the power line, or a filter is connected externally. For instance, a filter can be a choke placed between the load and the thyristor, and a capacitor connected to the load and a switching terminal of the thyristor. At high power levels, additional elements such as for example resistors, capacitors, special transformers (e.g., common mode chokes), may be necessary in order to mitigate noise—however, such filters can increase cost, size, weight, or heat loss of an associated product.
It is desirable to control rate of voltage change (dv/dt) across a thyristor during change of state (e.g., from off state to on state) such that filtering is not required to meet applicable noise emission standards. It is also desirable reduce cost, size, weight, and heat loss of a product employing thyristor(s).